Telephone trunk-circuits.



B, D. WlLLlS.

TELEPHONE TRUNK CIRCUITS.

APPLICATION FILED 2.06.23. i915,

1 ,267,03 1 Patented May 21, 1918. q, Q\N Nu if "N QUQ Q :3" @w g a &

L 1 I m -H l $3 P rumnno STATES PATENT OFFICE.

,J BERNARD D. WILLI ,'OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE TRUNK-CIECU1TS Specification of Letters Patent.

Patented May 21, 1918.

Application filed August 23, 1916. Serial No. 110,486.

To all whom it may concern lie it known that I, BERNARD l). winds, :1 citizen of the United States of America, and u resident of Chicago, county of Cook, and State of Illinois, have invented certain new and useful Improvements in Telephone Trunk-(-ircuits, of which the following is n specification.

My invention relates in. general to interoliire trunk circuits, but is more pa rticulurly concerned with circuits of this character which are adapted for use in uu'loinntie telephone systems. In U. S. Letters Patent $61,130,912, granted April 20. 1915, to T. (l. Martin, there is shown and described :1 two way trunk circuit for use in a two-wire or non-grounded automatic telephone system. The trunk circuit there illustrated is prorided with :1 repeater at" each end for transmitting operatin impulses to an automatic switch at the ot er end over the two sides of the lruui: line in series.

Such a trunk circuit is well adapted for use in a system in which the diflerent ofliccs or exchanges are only a few miles apart. In more extensive installations, however, comprising Widely scattered exchanges, which nnvv be separated by a hundred miles or more. it is advisable to lower the resistance of the impulse transmitting circuit by making use of a ground return The repeaters at each end, therefore, may be arranged to receive impulses transmitted over the two sides of a line in series. and repeat these impulses over a ground return circuit to up; pnrutns at the distant end. where the impuises are agointranslated to the series variety in order to o crate the usual twowu'o automatic switc ies. This method of operation, if special precautions are not taken, is open to the objection that the impulses are liable to be affected by variations in the ground potential at the opposite ends of the trunk circuit. In many localities the potential of ground may vary from negative values to fifteen or twenty volts above the ground potential at other points, which is suliicient to very seriously afiect the quality of impulses transmitted over ground return circuits, I

The object of my invention is to provide a trunk circuit of the general character set forth above which is adapted to autoinuticully compensate for any variations in the ground potential which may occur,

thereby securing accurate transmission of impulses regardless of such variations. The particular means employed to secure the foregoing results will be fully described hereinafter, and its operation explained, reference bein had to the accompanying drawing, whici shows diagrammutiea]ly a u-o-way automatic trunk circuit embodying the principles of my invention.

In the drawing, the reference characters 75 and indicate the two line conductors of the trunk circuit, which terminate at op posite ends in the windings of the repeat ing coils R and R Through the medium of repeating coil R the trunk conductors and 76 are inductively connected to condurtors l1 and 12, which in turn are adapted for connection either with conductors 5 and T or conductors 8 and 10, depending on the direction of the call. In a similar manner the repeating coil R serves to inductively connect the lineconductors 75 and 76 with conductors 111 and 112 which are adapted for connection either with conductors 105 and 107 or conductors 108 and 110.

The manner in which connections are established to or from the trunk circuit may he understood clearly by referring to the previously mentioned patent to Martin. Thus the bank contacts 2, 3, and 4 are assumed to be multiplied in the banks of first selector switches such as the one there shown and described, while the conductors 8, 9, and 10 extend to and terminate either in a line switch, as shown in the said Martin patent, or directly in a second selector switch. In the same manner, at the opposite end of the trunk circuit, the bunk contacts 102, 103, and 104 are multiplied in the banks of first I selectors in the distant exchange while the conductors 108, 109, and 110 extend either to a line switch or to a second selector switch.

The two groups of relays indicated col- Icctively by reference characters M and M comprise two repeaters through the medium of which the operating and talking circuits are established and controlled. It is thought that the functions of these relays can best be explained by describing the operations incident to the establishment of a connection over the trunk circuit. Accordingly it will be assumed that a calling subscriber has established connection through the medium ofinstrumentalities including a selector switch with the bank contacts 2, 3, and 4 for the purpose of connecting via the trunk circuit with a subscriber in the distant exchange.

Upon the completion of the connection to the bank contacts 2, 3, and l, the doublewound line relay 15 is energized over a circuit which may be traced as follows: ground at G, lower winding of line relay 15, and conductor 7 bank contact. -l. thence by way of the lower selector wiper (not shown), the callin subscribers loop and the upper selector wlper (also not shown), to the bank contact 2, and thence by way of conductor 5 and the upper winding of line relay 15 to the ungrouhded pole of battery B. ()n attracting its armature, the line relay 15 completes a circuit for the slow-aeting release relay 16 as follows: ground at Gr, armature 24 and its working contact, and winding of relay 16 to the ungroundcd pole of battery B. Upon energizing, relay lti prepares a circuit for relay 17 by means of the armature 26; switches the conductors 37 and 38 by means of armaturcs 28 and $29 from connection with the impulse receiving relay 19 into connection with contacts con trolled by the line relay 1!); and by means of armature 27 prepares a holding circuit for the selector switch which may be traced in part as follows: ground at G armature 27 and its working contact, and conductor 6 to bank contact 3, whence the circuit extends back to a relay in the selector switch which is maintained energized in the usual manner to prevent the release of the said selector.

As a further result of the energization of relays 15 and 16 a circuit has been completed for the impulse receiving relay 119 in the repeater M at the distant exchange. This is the circuit over which the operat ing impulses will be transmitted and it ox tends over the following path: ground at G windin 120 of relay 119, armatu'relQS and its bacE contact, conductor 137, Wind.- ing 133 of repeating coil R trunk line conductor 75, winding 33 of repeating coil R, conductor 37, armature 28 and its worl ing contact, armature 23 and its working contact, resistance 26, and battery B to ground at G". At the same time a circuit is completed over the lower trunk line .condoctor 76 which corresponds in every par ticular t0 the circuit just described except that it includes the lower winding 121 of relay 119 and that the battery B omitted. Assuming that the ground potentials at the two exchanges are the same, this latter circuit extending from ground G in one on change to ground G" in the other exchange will carry no current and may be for the present neglected.

Upon the completion. of the circuit through its winding 120, relay 119 is on ergized by current flowing over the trunk line conductor 75, and upon attracting its armature, completes an energizing circuit for the slow-acting relay 122 which may be traced as follows: ground at G, armature 152 and its working conta and winding of relay 122 to the ungrounded pole of battery 13. By the attraetirjln of armatures i530 and 151 of relay 1:52, the conductors 111 and 11L are shifted from connection with bank contacts 102 and ltl-t into connection with conductors 108 and 110, which latter conductors it will be HSSUlHCd terminate in the windings of the line relay of a second so lector switch This selector line relay will now be energized over a loop just completed by relay 119 and which may be traced as followsz conductor 108, armature 153 and its Working contact, and winding of impedance coil. 11%; to conductor 11tt On the energization of the selector line relay and the consequent i-nergization ol' the associated slow-acting release relay, the conductor 109 is grounded in the well known manner, whereby the repeater M" is protected against seizure by a first selector switch through the medium of the ground potential on bank contact 103 and its n'niltiplcs.

The foregoing operations have taken place as the result of the extension of the calling line to the repeater M, which ex tension may be assumed to have been accomplished by the calling subscriber through the ren'ioval of his receiver and the manipulation of his calling device in accordance with the first digit of the desired number. The calling subscriber may now operate his calling device in accordance with the second digit. of the desired number thereby resulting in a series of interruptions of the cireuit of the line relay 15. Responsive to these interruptions of its circuit the line relay i5 decnergizes a corresponding number of times and at the first dciinergization completes a circuit for the slow -acting relay 1? which may be traced as follows: ground at G, armature 2 1 and its back contact, armature 26 and its working contact and the winding of relay 17 to the ungrounded pole of the battery B. Relays 16 and 17, being slow-acting. retain their armatures during a series of irnp11lscs,after which relay 17 is deenergized. In its energized condition relay 17 by means of its armatures 30 and 30' opens the bridged windings of repeating coil R whereby the condensers 31 and 32 prevented from interfering with the transmission of impulses. It will be clear now that at each deencrgization of the line relay 15, the energizing circuit of the impulse receiving rcla 11!) at the distant exchange will be broken. Relay 119, there- Fore, vibrates its armature in synchronisin with the relay l5 and interrupts'at each debridge of said conductors at one enih {t connection from the middle point of said relay to ground, connections from the oi'i'icr end of said conductors to groin'ul, and u iizitiery in SQI'lOi-iii'lill one of said lust ground con ncctions.

5. In combination, :1 relziy comprising continuous winding in one (iii-cation ground ed at its niiddlc poini, line conductors coir necicd at one end, rcspertirely to opposito ends of said \iindiug, :2 battery, and means for connecting said lino conductors to ground at the other end and for including said battery in series with one of said con ductors.

i. In comliinutiim, a relay comprising it continuous winding in one direction ground ed at its n'iiddlc point, line conductors connected at one end, iirspcctively, to OppUBi i? ends of said winding, is luiitcry inning; it; positive pole grounded, and nit-nus for con necting suid line conductors at ihc other end, icsi'u clii'clyi in ground and t hron grounded pole of Slllil lottery.

in u iHlC TiEC-lh' syslmn a quounil w om circuit coiincciing wo [.X'Cllzlligflt :ind in illliilllg u vi'chiy in one cmhungc menus in the other exchange for trimsziiitiiug ci rrcnt impulses over said circuit to operate said ro lay. and iiutouuitic moans for prcvcnting diticrcnccs in. the ground. poirntizil ai the iwo cxch n s from interfering Will} the opcruii u of l relay.

l1. :1 ibijql'iilll5 system, :1 ground rciurn circuit connect ng two cxchungvs and including iii onecxchungo one winding of ii douiiilewound relay, means :it the Oliiul cl'uingc for transmitting current; iuipuiscs over said ciicuii to operate suid relay, and un :iui'oinu ic ground return ci'impcnsutiue; circuit also conucciing tho two excl-1m i and including the rccond winding: of 51ml rcluym .i'licrchy the said rein} is not zllllClfifid by dii crcni es in ground poly ii iul a l the two exchanges.

9. The combination with it relay and a ground return circuit thcrefmn of means for securing uniform operations of said relay unaii'ectcd, by varying; earth potentials, said means comprising a Second ground return circuit for said relay so connected that fluctuations of current in said first circuitdue to variations in earth potential are compcnsatcd for by corresponding fluctuations of current in said. second circiui'.

10. The fill'flnblllllirlOfl with a. relay provided wil 11 two windings, of separate ground return circuits for said windings, and :1 battery in one of said. circuits, said battery and relay windings being so connected that r-urrcni's in the circuit containing tho battery caused by unequal ground potentials are counter-1miunced by corresponding currents in the othcr circuit.

'11 In a telephone system, means for repcuting current impulses from one exchange to zinothcr, said means comprising a ground return circuit including a. battery at one end and one winding of a relay at the other end, nnil ii second ground return circuit includin u second winding of said relay, whereby ilili'i-rences in ground potential between the two exchanges which oppose or assist the rurrcni from said buttery also cause com-- pcnsuting cur-units to flow in said second cir- :uii.

12. In ii telephone system, an impulse transmitting relay and. a. differential iin pulse receiving relay, two opposing ground min-n circuits for the latter relay controlled hy the former relay, and :1 battery in one of will circuits.

1:}. The combination with a relay hiivin Luo \i-indings, of separate circuits for= aiiifi ii nuiings having a common conductor, sin fll iifl'itiillg lillltil in one of said circuits out" side the conunon conductor, and means for 'ii iiillg u SCl'iGb of interruptions in said -'i|' 'ut. in hpiflitltl said relay intermittently.

i. The combination with a relay pro mm with two windings, oi seperate cirunits {or said windings having a common mirth return, a battery in one of said circuits only, the other circuit cruistituting a path for the flow of earth currents unopposed b artificial sources of poicntial, and means 2i)! producing a series of interruplions in said circuits to operate. said relay intermittent! 15. The combination with a trunk line connecting two exchanges, of a relay providcd with two windings in one exchange, a battery in the other exchange for operating said relay, ground return circuits for the said relay wii'idiugs including, respectively one conductor oi. said trunk line and sail buttery, and the other conductor of said trunk line exclusive of said battery, and means for reducing a series of interruptions in suit circuits to operate 'said relay intermittcutly.

16. The combination with a relay provided with two windings, of separate ground return circuits for said windings a battery in one of said circuits, said battery and relay windings being so connected that currents in. the circuit containing the battery cullscdb unequal ground potentials are counter-bu anccd by corresponding currents in the other circuit, and means for producing a series of interruptions in said circuits to operate said relay intermittently.

17. The combination with a relay having two windings, of separate circuits for said windings ha ing a common cimduvtor, a huttery for o 'uiaitmg suid relay in NH" f said circuits outside the common couillulin' it third circuit under the coniml of wi l i s-i relay, and a second relay for produc ng .1 series of inberruptioim in said circuits to ener tion the reviously described controlling circuit 0 the selector switch in which the conductors 108 and 110 terminate. In this manner the selector switch is controlled to extend the connection in accordance with the second digit of the called number. It is understood that the slowacting relay-L2 remains energized during the momentary eenergiza'tions of relay 119.

The remainlng di 'ts of the desired number may now be ca ed one after the other and are repeated b the relays l5 and 119 to successive switc es in the distant exchange in the manner just described until finally the connection is completed to the called subscribers line. Thereafter the usual instrumentalities are brought into play to effect the signaling of the called subscriber and conversation may then be held over the completed connection in thecustomary manner. For the sake of clearness the talking conductors of the trunk circuit have been shown in hoavy'lines.

The foregoing is descriptive of the opera-- tion when the ground connections at the re spective exchanges are at the same potential. It will now be assumed that due to the eifect of street railway currents or other agencies, the ground at G and G is at a higher ,otential than the ground at G. This di erence of potential will be in opposition to the potential of the battery B and the current flow over the trunk line conductor and through the winding 120 of relay 119 will therefore be. reduced. Such reduction of current flow in the winding 120 would seriously. affect the operation of relay 119 were it n'bt-for the provision of the compensating circuit, over which current now flows as flows: 'ound at G, resistance 35, armature 25 and its working contact, armature 29 and its working contact, winding 34 of repeating coil R, trunk line conductor 76, winding 134 of repeating coil R armature 129 and its back contact, and the winding 121 of relay 119 to ound at G". The direction of current ow in winding 12]. is

such that it assists the current in winding 120, whence it will be seen that the loss of currentin the one winding is compensated as by a current in the other winding.

Assuming now that the potential at ground G" is higher than the otential of ground at the other excha e,t is difference in potential will be atlde to the" potential of the battery 13 and the cur nt'in winding 120 of relay'119 will accordin ly be increased. But this difference in potential also results in. a

current in they lower, winding 120of relary 119 via the path previously traced except that now the current flow is in'the reverse direction. Currents in the two windings of relay 119 now oppose each other, whence it will be clear that the effect of the increased current in winding 121) is counteracted by said windi It has been already mentioned that the trunk circuit shown is adapted for two way operation. Since the equipment at one end is an exact duplicate of the equipment at the other end it is not thought to be neces sary to explain in detail the operations which take place when the call is in the other direction. It may be stated, however, that the bank contacts 102, 103, and 104: may be seized by a selector switch, assuming, of course, that the trunk circuit is idle, after which the line relay 115 is operated inrespouse to interruptions of the calling line to transmit impulses to the impulse receiving relay 19 at the other end of the trunk circuit. Relay 19 in turn operates to control a series of automatic switches over the condoctors 8 and 10.

It will be seen from the foregoing that I have devised an exceedingly simple and ellicient. trunk circuit comprising a ground return impulse transmitting circuit, together with means for automatically compensating for differences in the ground potentials at opposite ends thereof.

While I have shown and described a certain specific embodiment oi. my invention I consider it probable that modifications may be made in order to adapt the invention for use in other telephone systems, or even for other purposes 3. together. I do not, there fore, wish to limit myself to the precise form shown, butdesire rather to include and have protected by Letters Patent all forms and modifications of my invention which come within the scope of the appended claims.

What I claim as my invention is:

1. The combination with a relay having two windings, of separate circuits for said windings having a common conductor, and a battery for operating said relay in one of said circuits outside the common conductor.

2. The combination with a relay provided with two windings, of separate circuits for havin a common earth return, and a attery in one of. said circuits only, the other circuit constituting a path for the flow of earth currents unopposed by artificial sources of potential.

3. The combination with a trunk line connecting two exchanges, of a relay provided operate said lirsl. relay intermittently, whereby corresponding interruptions are produced in said third circuit.

18. The combination with a relay provided with two windings of separate circuits for said windings having a common earth re turn.,a battery in one of said circuits only, the other circuit constituting a path for the flow of earth currents unopposed by urtificial sources of potential, at hii dficireuit under the, control of said first relay, and a second relay for producin;,, a series of interruptions in said circuits to operate said first relay intermittently, whereby corres onding interruptions are produced in said t iird circuit.

19. The combination with a trunk line connecting t-wo exchanges, of a relay provided with two windings in one exchange a battery in the other exchange for operating said relay, ground return circuits forthe said relay windings including, res ectively, one conductor of said trunk line and said battery, and the other conductor of said trunk line exclusive of said battery, 9. third circuit under the mnlrol of said lirst relay, and a second rein) for producing a series of interruptions in aid circuits to operate said first relay intvrmittcntlr, whereby corresponding iliiclillptiolh are produced in said third circuit.

20. The omliinnt ion with a relay proridcd with two windings. ol separate ground return circuits for said windings, a battery in one of said circuits, said battery and relay windings being -o connected that cnrrcnls in the circuit containing the batter caused by unequal ground iotrntials are counterbalanced by corresponding currents in the other circuit. a third circuit under the control of said first relay, and a second relay for producing a series of interruptions in said circuits to operate said first relay intermittcntlywhereby rorrespomlin r interruptions are produced in said third circuit.

Signed by me at Chicago, Cook county, State of Illinois, this 1th day of August, 1916.

BERNARD n. WILLIS. 

